This is a game of accumulation. The rule is don't sell if you're not sure you could rebuy the same amount of bitcoins or more at a cheaper price. Gains are most likely diminishing but on the bright side the big crashes are also rarer and less pronounced. So probably a safe sell zone is anything above 150k and don't sell anything below 60k, because we might never ever get below that once we go past it even at a bottom of the next bear market. An 80% crash like the last cycle is less likely to happen. Inferring 2018 crash is less severe than 2014 crash (the first cycle).